Insulin-like androgenic gland factor regulates the development of internal and external secondary sexual characteristics in juvenile male kuruma prawn Marsupenaeus japonicus

In decapod crustaceans, insulin-like androgenic gland factor (IAG) is considered a key regulator of male sexual differentiation and maturation. In the kuruma prawn Marsupenaeus japonicus, an important fishery species in Japan, a homologous molecule, Maj-IAG, has been identified. However, its physiological functions in males remain poorly understood. In this context, we conducted Maj-IAG knockdown (KD) via RNA interference for nine weeks in juvenile male M. japonicus. Double-stranded RNA was administered by injection five times at two-week intervals, with the dosage increased according to juvenile growth. As a result, Maj-IAG KD was successfully achieved, with an average reduction of approximately 65 % in expression level compared with controls at week nine. Maj-IAG KD significantly inhibited the development of the petasma, male-specific external copulatory structure, and parts of the internal reproductive organs, such as the vas deferens and seminal vesicles. In contrast, somatic growth and testicular development were unaffected by Maj-IAG KD. Histological analysis of the testes revealed no evident abnormalities such as degeneration of testicular structures or abnormal arrest of germ cell differentiation. These findings indicate that Maj-IAG partially governs the development of male secondary sexual characteristics in juveniles and further suggest that once testicular differentiation is initiated, the maintenance and development of the testis proceeds without dependence on Maj-IAG. Our study provides fundamental insights that may contribute to the advancement of functional sex reversal technologies in penaeid shrimps.